Synthesis and properties of carbon microspheres based on tannin–sucrose mixtures treated in hydrothermal conditions

Abstract

Sustainable carbon materials have been synthesised by use of inexpensive natural precursors, tannin and sucrose, mixed in aqueous solution in various proportions (from 0:1 to 1:0), and then submitted to hydrothermal carbonisation (HTC) at various pH (from 2 to 8) and temperatures (160, 180 or 200 °C). The resultant hydrochars were finally pyrolysed at 900 °C under nitrogen flow to produce highly porous carbon materials with BET areas as high as 810 m2/g without activation. The effects of the initial tannin/sucrose weight ratios and of the HTC conditions were investigated in terms of final particle size (from 1 to 10 μm), carbon yield (from 30 to 45%), composition (C from 88 to 93 wt.%; O from 6 to 10 wt.%), surface chemistry (C from 88 to 98 at.%; O from 2 to 12 at.%) and porous texture (NLDFT surface areas and micropore volumes from 840 to 1420 m2/g and from 0.23 to 032 cm3/g, respectively). All these parameters were discussed and correlated with the electrochemical properties of the same materials. Special attention was paid to the separate roles of porosity and surface chemistry, and on the reversibility of the electrochemical reactions.